This invention related to a service riser, particularly for use in the gas supply industry.
Gas is increasingly supplied through plastics pipes, especially polyethylene pipes although not exclusively so. The main advantage of plastics pipes is their resistance to corrosion and their flexibility. However where a plastics pipe is buried underground and rises to the surface to supply a house or other establishment, it is desirable to shield it. Also, of course, it requires an adapter at its end for connection to a meter or other equipment in the house. Indeed there are various regulations in different jurisdictions that require this additional protection at the transition from under- to over-ground.
Numerous patents describe such systems. For example U.S. Pat. No. 4,482,170 (Jacobson et al) discloses gas riser apparatus in which a metal tube is swaged to produce an internal step. The plastics pipe is terminated with an internal strengthening sleeve (to give the pipe radial compression strength), a collar then being swaged down around the end of the pipe, teeth on the collar biting into the plastics material. The end of the pipe is then pulled back into the metal tube with the collar then squeezing between itself and the internal step an elastomeric seal ring which thus seals the tube against the pipe. The tube then becomes the gas carrier and usual connection means are provided on the end of the tube for connection to a meter etc. The tube is finally indented or pinched onto the collar to retain the collar in position.
The tube is generally of mild steel meeting specific requirements but, usually, it has quite a wide tolerance on its dimensions. Thus, for example, a thread typically formed on its end is frequently tapered, at least partly so as to accommodate these wide tolerance.
U.S. Pat. No. 4,801,159 (Seborn) discloses another suitable arrangement, not dissimilar to the above-described arrangement. Other arrangements are disclosed in U.S. Pat. No. 4,519,634, U.S. Pat. No. 5,590,914 and EP-A-0539728.
Because the metal tube is at least partly taken underground it is necessary that it be provided with effective environmental protection. This is normally afforded by coating with an epoxy resin or the like or by galvanising the tube. In such a case a minimum of reworking should be effected when connecting the tube to the end of the gas pipe to avoid disturbing the environmental protection. However, some methods involve fitting an adapter to the end of the pipe and then welding the adapter to the tube. This of course renders re-application of protection necessary.
It is therefore an object of the present invention to provide a riser which is simple to construct, meets all relevant standards and requirements and has minimum disruption of the environmental seal.